Can the court consider a child testimony as an evidence even when the interviewer used leading questions? I am wondering if there's any law that force the court to reject child testimony if the interviewer used leading questions, or if it's up to the court to decide whether to reject it or not. Do they have that discretion or not?
If the court thinks it is not appropriate to use leading questions when (cross-)examining a child, it will disallow them to be asked. If the question has been voiced already, the judge may tell the child witness not to answer. If the witness has answered already, the judge may direct the jury to disregard that answer.
However, if the judge does not intervene (or expressly allows the question), then the given answer gets accepted as evidence: it won't be ruled out post-factum.
Note that the judge may not initially care/think that the question is inappropriate, but agree upon the other party raising an objection ("sustain" the objection).